ATLANTA — As President Obama moves forward with plans to punish the regime of Syrian President Bashar al-Assad for using chemical weapons, the battle for war resolve in Congress is coming down to the American grass roots – in particular, a tea party movement emerging as arguably the country’s strongest antiwar voice.

“We share the humanitarian concern for the Syrian people … but we strongly believe the situation in Syria will not improve, and could well deteriorate, due to American military involvement,” Bruce Carroll, chairman of a tea party group called Carolina Conservatives United, told Breitbart News on Friday. He added that “Obama has not adequately made the case that any national security interests are at stake.”

The idea of right-wing conservatives heading up antiwar protests is eye-opening, though critics question whether it’s a genuine philosophical viewpoint or simply more political obstructionism of Mr. Obama’s agenda.

Still, the reversal is notable. After all, it was progressives who led protests against the Afghanistan and Iraq wars, with Obama emerging as a chief critic of the Bush doctrine in his campaign for president.

What’s now coalescing is an ad hoc coalition of tea party conservatives and antiwar liberals, brought together by what the Washington Post’s Greg Sargent calls “some civil libertarian overlap” around concerns about overreach in domestic spying by government agencies.

The upshot is that the “wing” grassroots in both parties is fomenting opposition to leadership, representing “a genuine threat to the outcome,” writes Mr. Sargent. One sign: Tea party loyalists forced minority leader Sen. Mitch McConnell (R) of Kentucky to remain neutral on the intervention (so far, at least), after they threatened him with a primary challenge.

Obama, having established a “red line” on the use of chemical weapons in Syria last year, appeared set to launch strikes last week, but pulled back amid growing bipartisan concerns. After tense hearings on Capitol Hill this week, Obama is now seeking Congressional approval, setting off frantic “whip-counting” in Congress over whether he has the votes.

Several key Republicans, including House Speaker John Boehner, have supported Obama’s plan, joining Democrats like Rep. Nancy Pelosi in backing plans for a strike.

Meanwhile, a progressive Democrat, Rep. Alan Grayson, is leading an ad hoc whip count that is aligning antiwar liberals with antiwar libertarians such as Sens. Rand Paul of Kentucky and Mike Lee of Utah. In June, Mr. Rand and Mr. Lee joined Democrats Chris Murphy of Connecticut and Tom Udall of New Mexico to sponsor a bill barring the Obama administration from “supporting … military or paramilitary operations in Syria.”

“It’s not coincidental that the failure of the war rhetoric is happening in both parties, but rather reflects a growing unity among Progressive Democrats and the Tea Party Republicans, each of which is more than willing to stand up to the party’s leadership, and stand with an American public that polls show is also opposed to war,” writes Jason Ditz on AntiWar.com.

Often seen as simply obstructionist, the tea party’s opposition to action in Syria gives the loosely organized and lately quiescent movement a shot at a more deeply philosophical argument that could resonate even among Americans who have been critical of the movement.

“The talk of war in Syria has offered Tea Party lawmakers a unique chance to position themselves as the voice of reason on national security,” writes Julian Pequet for The Hill newspaper.

“The things I’m seeing and emails I’m getting from folks around the state, they’re not in favor” of a US attack in Syria, John Kemper of the United Kentucky Tea Party told Mother Jones.

To be sure, some critics see simple obstructionism, not philosophical fundamentals, in the emerging antiwar wing of the right, suggesting that the antiwar push is simply part of a philosophy that sees any federal government action as illegitimate.

“Whether it is wise or prudent to employ … forces is always the most legitimate of questions,” writes the Washington Post’s Harold Meyerson. “Whether the nation should halt such actions, or the payment of its pensions and health-care obligations, because the government should stop functioning altogether … until Obamacare or Obama or modernity just go away is not.”

Nevertheless, the merging of the most extreme wings of both political parties over action in Syria comes amid simmering concerns among many Americans of illegal spying by the National Security Agency. “That’s what hits the nerve within the general tea party – excessive use of the president’s power,” Tea Party Express strategist Sal Russo tells the Hill.

Syria is involved in a bloody civil war between Baath loyalists and Islamist rebels, sparked at least in part by the region-wide Arab Spring. Over 100,000 people have been killed, some, the Obama administration alleges, in chemical attacks ordered by the Assad regime.

“I know that the American people are weary after a decade of war, even as the war in Iraq has ended, and the war in Afghanistan is winding down,” Obama said in his weekly radio address Saturday. “But we are the United States of America. We cannot turn a blind eye to images like the ones we’ve seen out of Syria.”